sheets should be stacked on the larger ones to avoid unsupported overhead. Storage of transparent plastic sheets presents no special fire hazard, as they are slow burning. Masking paper should be left on the plastic sheet as long as possible. You should take care to avoid scratches and gouges, which may be caused by sliding sheets against one another or across rough or dirty tables. Formed sections should be stored so that they are amply supported and there is no tendency for them to lose their shape. Vertical nesting should be avoided. Protect formed parts from temperatures higher than 120°F. Protection from scratches may be provided by applying a protective coating of masking paper or other approved materials. If masking paper adhesive deteriorates through long or improper storage, making removal of paper difficult, moisten the paper with aliphatic naphtha, which will loosen the adhesive. Sheets so treated should be washed immediately with clear water. CAUTION Aliphatic naphtha is highly volatile and flammable. You should exercise extreme care when using this solvent. Do not use gasoline, alcohol, kerosene, xylene, ketones, lacquer thinners, aromatic hydrocarbons, ethers, glass cleaning compounds, or other unapproved solvents on transparent acrylic plastics to remove masking paper or other foreign material, as these will soften and/or craze the plastic surface. NOTE: Just as woods split and metals crack in areas of high, localized stress, plastic materials develop, under similar conditions, small surfaces fissures called “crazing.” These tiny cracks are approximately perpendicular to the surface, very narrow in width, and usually not over 0.01 inch in depth. These tiny fissures are not only an optical defect, but also a mechanical defect, inasmuch as there is a separation or parting of the material. Once a part has been crazed, neither the optical nor mechanical defect can be removed permanently; therefore, prevention of crazing is a necessity. When it is necessary to remove masking paper from the plastic sheet during fabrication, the surface should be remasked as soon as possible. Either replace the original paper on relatively flat parts or apply a protective coating on curved parts. REINFORCED PLASTICS Glass fiber reinforced plastic and honeycomb are used in the construction of radomes, wing tips, stabilizer tips, antenna covers, fairings, access covers, etc. It has excellent dielectric characteristics, making it ideal for use in radomes. Its high strength/weight ratio, resistance to mildew and rot, and ease of fabrication make it equally suited for other parts of the aircraft. The manufacture of reinforced plastic laminates involves the usc of liquid resins reinforced with a filler material. The resin, when properly treated with certain agents known as catalysts, or hardeners, changes to an infusible solid. The reinforcement materials are impregnated with the resin while the latter is still in the liquid (uncured) state. Layers or plies of cloth are stacked up and heated under pressure in a mold to produce the finished, cured shape. Another technique, culled “filament winding,” consists of winding a continuous glass filament or tape, impregnated with uncured resin, over a rotating male form. Cure is accomplished in a manner similar to the woven cloth reinforced laminates. Glass fiber reinforced honeycomb consists of a relatively thick, central layer called the “core” and two outer laminates called “facings.” (See figure 1-22.) The core material commonly used in radome construction consists of a honeycomb structure made of glass cloth impregnated either with a polyester or epoxy or a combination of nylon and phenolic resin. The material is normally fabricated in blocks that are later cut on a band saw to slices of the exact thickness desired, or it may be originally fabricated to the proper thickness. The facings are made up of several layers of glass cloth, impregnated and bonded together with resin. Each layer of cloth is placed in position and impregnated with resin before another layer is added. Thicker cloths are normally used for the body of the facings, with one or more layers of liner weave cloth on the surface. The resins are thick, syrupy liquids of the so-called contact-pressure type (requiring little or no pressure during cure), sometimes referred to as contact resins. They are usually thermosetting polyester or epoxy resins. Cure can be affected by adding a catalyst and heating, or they can be cured at different temperatures by adjusting the amount and type of catalysts. Inspection 1-43